Calibration Clock Output; Alarm Output; Rtc Low Power Modes; Table 80. Effect Of Low Power Modes On Rtc - STMicroelectronics STM32F05 series Reference Manual

Real-time clock (RTC)
24.3.14

Calibration clock output

When the COE bit is set to 1 in the RTC_CR register, a reference clock is provided on the
RTC_CALIB device output.
If the COSEL bit in the RTC_CR register is reset and PREDIV_A = 0x7F, the RTC_CALIB
frequency is f
frequency at 32.768 kHz. The RTC_CALIB duty cycle is irregular: there is a light jitter on
falling edges. It is therefore recommended to use rising edges.
When COSEL is set and "PREDIV_S+1" is a non-zero multiple of 256 (i.e: PREDIV_S[7:0] =
0xFF), the RTC_CALIB frequency is f
calibration output at 1 Hz for prescaler default values (PREDIV_A = Ox7F, PREDIV_S =
0xFF), with an RTCCLK frequency at 32.768 kHz.
24.3.15

Alarm output

The OSEL[1:0] control bits in the RTC_CR register are used to activate the alarm alternate
function output RTC_ALARM, and to select the function which is output. These functions
reflect the contents of the corresponding flags in the RTC_ISR register.
The polarity of the output is determined by the POL control bit in RTC_CR so that the
opposite of the selected flag bit is output when POL is set to 1.
Alarm alternate function output
The RTC_ALARM pin can be configured in output open drain or output push-pull using the
control bit ALARMOUTTYPE in the RTC_TAFCR register.
Note: Once the RTC_ALARM output is enabled, it has priority over RTC_CALIB (COE bit is don't
care and must be kept cleared).
When the RTC_CALIB or RTC_ALARM output is selected, the RTC_OUT pin is
automatically configured in output alternate function.
24.4

RTC low power modes

Table 80.
Mode
Sleep
Stop
Standby
548/742
/64. This corresponds to a calibration output at 512 Hz for an RTCCLK
RTCCLK
Effect of low power modes on RTC
No effect
RTC interrupts cause the device to exit the Sleep mode.
The RTC remains active when the RTC clock source is LSE or LSI. RTC alarm, RTC
tamper event, RTC timestamp event, and RTC Wakeup cause the device to exit the Stop
mode.
The RTC remains active when the RTC clock source is LSE or LSI. RTC alarm, RTC
tamper event, RTC timestamp event, and RTC Wakeup cause the device to exit the
Standby mode.
Doc ID 018940 Rev 1
/(256 * (PREDIV_A+1)). This corresponds to a
RTCCLK
Description
RM0091